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JP3612365B2 - Active cathode and method for producing the same - Google Patents

Active cathode and method for producing the same Download PDF

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Publication number
JP3612365B2
JP3612365B2 JP12591195A JP12591195A JP3612365B2 JP 3612365 B2 JP3612365 B2 JP 3612365B2 JP 12591195 A JP12591195 A JP 12591195A JP 12591195 A JP12591195 A JP 12591195A JP 3612365 B2 JP3612365 B2 JP 3612365B2
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layer
cathode
platinum
nickel
ruthenium
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JPH08296079A (en
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剛陸 岸
修 有元
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ThyssenKrupp Nucera Japan Ltd
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Chlorine Engineers Corp Ltd
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Priority to US08/634,355 priority patent/US5954928A/en
Priority to EP96106628A priority patent/EP0739999B1/en
Priority to DE69611476T priority patent/DE69611476T2/en
Publication of JPH08296079A publication Critical patent/JPH08296079A/en
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    • C23C28/00—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D
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    • C23C28/021—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D only coatings only including layers of metallic material including at least one metal alloy layer
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C28/00—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D
    • C23C28/02—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D only coatings only including layers of metallic material
    • C23C28/023—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D only coatings only including layers of metallic material only coatings of metal elements only
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C28/00—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D
    • C23C28/30—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer
    • C23C28/32—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer including at least one pure metallic layer
    • C23C28/321—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer including at least one pure metallic layer with at least one metal alloy layer
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C28/00—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D
    • C23C28/30—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer
    • C23C28/32—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer including at least one pure metallic layer
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    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
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    • C25B11/04—Electrodes; Manufacture thereof not otherwise provided for characterised by the material
    • C25B11/051—Electrodes formed of electrocatalysts on a substrate or carrier
    • C25B11/073—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material
    • C25B11/091—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material consisting of at least one catalytic element and at least one catalytic compound; consisting of two or more catalytic elements or catalytic compounds

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  • Inorganic Chemistry (AREA)
  • Electrochemistry (AREA)
  • Electrodes For Compound Or Non-Metal Manufacture (AREA)
  • Chemically Coating (AREA)
  • Other Surface Treatments For Metallic Materials (AREA)

Description

【０００１】
【産業上の利用分野】
本発明は活性陰極及びその製造法に関し、詳しくはハロゲン化アルカリ金属、水酸化アルカリ金属等のアルカリ金属塩の水溶液を長期間低水素過電圧で電気分解することができる活性陰極及びその製造法に関する。
【０００２】
【従来の技術】
隔膜法、イオン交換膜法等でハロゲン化アルカリ金属水溶液又は水酸化アルカリ金属水溶液を電気分解する場合、従来、陰極としては軟鉄を主体とする材料が使用されている。これらの電気分解においては陰極で水素が発生し、軟鉄は水素過電圧が高いという欠点があるため、軟鉄を主体材料とする陰極の過電圧より低い水素過電圧を示す活性陰極が種々提案されている。従来提案の活性陰極は、ニッケル、コバルト、白金族元素の金属単体又はそれらの混合物又はそれらの酸化物が材料として用いられ、一般に、これら材料の被膜が軟鉄等の金属基体上に形成されているものであり、被膜の形成方法としては、電気メッキ法、無電解メッキ法、分散電気メッキ法、溶射法、浸漬法等が提案されている。例えば、ラネーニッケル単体またはラネーニッケルと水素吸蔵合金を複合メッキした活性陰極（特公昭６１−１２０３２号公報、特公昭６１−３６５９０号公報）や、酸化ニッケル又は酸化コバルトを溶射したもの（特公昭６３−６４５１８号公報、特公平３−３５３８７号公報）がある。
【０００３】
【発明が解決しようとする課題】
活性陰極において、最も重要な点は、過電圧が低く保持できることは勿論、電解槽の停止や解体時に劣化することがなく、また、イオン交換膜法電解槽においてゼロギャップで使用する場合に、イオン交換膜がニッケル等被膜材により汚染が起こらないこと、更に製造コストが安価であるということである。
しかしながら、従来提案の低水素過電圧において、例えば、前記のラネーニッケル単体やラネーニッケルと水素吸蔵合金との複合金属をメッキした活性陰極は低水素電圧を保持するが、イオン交換膜がニッケルにより汚染されたり電解槽を解体し活性陰極が空気と接触することにより酸化され発火したり劣化する欠点がある。また、酸化ニッケル又は酸化コバルトを溶射したものは、電解槽が解体され活性陰極が空気と接触しても酸化して劣化しないが、水素過電圧がラネーニッケル単体等の活性陰極より高い上、水素過電圧が経時的に上昇するという欠点がある。
【０００４】
また、従来、低水素過電圧を示す活性陰極の一つとして、白金族金属による被膜形成も提案されているが、単に平滑な金属基体の表面を白金族で被覆するというものであり、金属基体と白金、ルテニウム等の白金族金属との付着は弱く、白金族金属被膜が基体から剥離し易く問題となっていた。また、表面活性を高めるためには大量の白金族金属が必要となり経済的問題もある等により、従来、白金族金属を主体とする活性陰極については、十分な検討がなされていなかったのが実状である。
本発明は、上記の従来の活性陰極の現状に鑑み、イオン交換膜への汚染がなく、酸化反応による劣化や発火のおそれがなく、且つ、十分に低い水素過電圧を保持できる活性陰極及びその製造法を提供することを目的とする。更に、従来提案の活性電極の長所を維持しつつ、その欠点が解消された活性陰極及びその製造法の提供を目的とする。即ち、例えば、ラネーニッケル単体又はラネーニッケルと水素吸蔵合金を複合メッキした活性陰極に関しては、イオン交換膜のニッケル汚染を防止でき、電解槽解体においても活性陰極の酸化を抑止し発火や劣化を防止することができ、また、酸化ニッケル又は酸化コバルトの溶射被膜した活性陰極に関しては、水素過電圧を低下させることができるようにすることである。
【０００５】
【課題を解決するための手段】
本発明によれば、金属基体上に、ニッケル又はコバルトを主体とする第一層及び該第一層上に白金またはルテニウムを主体とする第二層が形成されてなることを特徴とする活性陰極が提供される。
上記本発明の活性陰極において、前記第一層がラネーニッケルを有して形成されてなり、前記第二層が広大な陰極作動面積を有することが好ましい。また、前記第一層が酸化ニッケル又は酸化コバルトを有して形成され、前記第二層が微細な白金粒子又はルテニウム粒子により形成されて広大な陰極作動面積を有することが好ましく、これら白金粒子又はルテニウム粒子が、０．００１〜０．０１μｍであることが好ましい。更に、前記陰極作動面積が、陰極の投影面積１ｍ２ に対し３０〜３０００倍であることが好ましい。
また、本発明は、金属基体上に金属ニッケルを主体とする第一層が形成されてなる陰極基体を、白金塩またはルテニウム塩の溶液に浸漬処理して該第一層上に白金またはルテニウムを主体とする第二層を被覆することを特徴とする活性陰極の製造法を提供する。
更に、本発明は、金属基体上にニッケル又はコバルトを主体とする第一層が形成されてなる陰極基体を、白金塩またはルテニウム塩の溶液に浸漬し、更に、電解処理して該第一層上に白金またはルテニウムを主体とする第二層を被覆することを特徴とする活性陰極の製造法を提供する。
上記本発明の活性陰極の製造法において、前記第一層が電気メッキ法、無電解メッキ法、分散電気メッキ法、溶射法、又は浸漬法により形成されることが好ましい。
なお、本発明において陰極作動面積とは、陰極の外見上の面積（投影面積）とは異なり実質的に陰極として作動可能な部分の表面積をいう。
【０００６】
【作用】
本発明の活性陰極は上記のように構成され、特に金属基体上にラネーニッケルや酸化コバルト等のニッケルまたはコバルトを主体とする第一層を形成した上に、更に、化学的に安定な白金又はルテニウムで、また、要すれば微細な白金粒子またはルテニウム粒子で第二層を形成して第一層表面を被覆するため、広大な陰極作動面積を有し低水素過電圧を保持できる。また、例えばラネーニッケル等の高表面積を有する陰極表面が被覆されることから、イオン交換膜のニッケル汚染を防止できると共に、反応活性の高いニッケル系表面は、電解槽の停止時や解体時においても酸素との接触がないことから陰極の劣化もない。
また、本発明の活性陰極において、活性の乏しい表面状態の酸化ニッケルや酸化コバルトにより形成される第一層は水素過電圧が比較的高くなるが、その表面を水素吸蔵性であり活性の高い微細な白金粒子やルテニウム粒子で被覆してなることから、その水素過電圧を低下させることができる。
本発明の活性陰極は、電解槽停止時等にいわゆる逆電流が流れ陰極が陽分極した場合でも、白金は容易には酸化されないため、また、ルテニウムは酸化されるが再通電により容易に還元されルテニウムとなるため、活性が損なわれることなく安定である。また、白金及びルテニウムは、双方共、ニッケルより化学的耐久性に優れているため、ニッケル主体の第一層を白金またはルテニウムにより被覆することにより、イオン交換膜をニッケル汚染から防止することができる。
更に、本発明の上記活性陰極は、電気メッキ、分散メッキ等従来公知の方法により金属基体上に第一層を形成した後、更に、白金又はルテニウムの塩類の溶液中に浸漬、または、浸漬後電解処理することにより広大な陰極作動面積を有する第二層を形成することができ、従来の活性陰極を用いてより安定な水素過電圧の低い活性陰極を得ることができる。
【０００７】
以下、本発明について詳細に説明する。
本発明で使用する金属基体の材質は、特に制限されるものでなく、通常、ステンレス鋼、ニッケル、コバルト、鉄鋼を用いることができる。また、金属基体の構造としては、平板状、エキスパンドメタル状、穿孔板状、網状、棒状等が使用でき、特に限定されない。
【０００８】
本発明の第一層は、上記金属基体上に形成されるニッケルまたはコバルトを主体とする層であり、従来提案されている活性陰極と同様にして形成されたものを用いることができる。ニッケルを主体とする第一層としては、ラネーニッケル、ラネーニッケルと水素吸蔵合金とから形成される層、ニッケルと錫の合金、ニッケルとクロムの合金等のニッケル合金の層、硫黄含有ニッケル、活性炭及び硫黄含有ニッケル等の他成分含有ニッケルの層、または酸化ニッケル層等の従来のニッケル系活性陰極としての表面層を用いることができる。ラネーニッケル、ラネーニッケルと水素吸蔵合金とから形成される表面層は、高表面積を有し高活性であるため好ましい。コバルトを主体とする第一層は、従来提案の酸化コバルト層の活性陰極の表面層を用いることができる。
上記の第一層は、通常の電気メッキ法、無電解メッキ法、分散電気メッキ法、溶射法または浸漬法で形成することができ、ニッケルまたはコバルトの構成成分に応じ適宜選択すればよい。第一層の厚さは、１０〜５００μｍであればよく、適宜選択することができる。通常、５０〜３００μｍである。
【０００９】
本発明の活性陰極の第二層は、上記第一層表面を白金族金属の白金またはルテニウムで被覆して形成される層である。第二層は、下記するように白金またはルテニウムの塩類を溶解した水溶液中に、金属基体上に上記第一層が形成されたいわゆる従来型活性陰極を浸漬、または浸漬して電解処理することにより形成することができる。本発明において、ニッケル主体の第一層表面は、白金及びルテニウムで構成される第二層により被覆されることにより、ニッケルより白金、ルテニウムは化学的耐久性に優れ、イオン交換膜をニッケル汚染から回避できる。
本発明の活性陰極の第二層は、広大な陰極作動面積を有することが好ましく、そのためには高表面積を有するように形成する。広大な陰極作動面積とは実質的に陰極として作動する表面積をいい、活性陰極の外見上の単位面積当たり、即ち、陰極の投影面積１ｍ２ に対して約３０〜３０００倍の広さの表面積を有することが好ましい。本発明の活性陰極は、上記のような広大な表面積を有することにより陰極作動面積が広がるため、実質的に陰極電流密度が低下し、その結果水素過電圧を低下させることができる。
本発明の第二層の広大な表面積は、下層の第一層の形態により適宜選択するが、例えば、第一層が酸化ニッケルや酸化コバルトの酸化物系である場合には、一般に０．００１〜０．０１μｍの微細な白金粒子またはルテニウム粒子を、白金またはルテニウムの塩類を溶解した水溶液中で電解する等の方法を用いて被覆することにより形成することができる。また、第一層がラネーニッケルやラネーニッケルと水素吸蔵合金等のラネーニッケルを含む層である場合は、第一層自体が高表面積であり、その表面に第二層の白金またはルテニウム被膜を白金またはルテニウムの塩類を溶解した水溶液中に浸漬または浸漬して電解処理する等の方法で形成することにより、広大な表面積を有する第二層を形成することできる。
【００１０】
本発明の活性陰極は、上記のように金属基体上に、ニッケルまたはコバルトを主体とする第一層及び白金またはルテニウムの第二層が順次形成されてなるものであり、従来の活性陰極表面、即ち第一層が白金族金属の白金またはルテニウムにより被覆され、陰極表面が高活性で且つ安定な白金またはルテニウムに置き換わるため水素過電圧が著しく低下する。
また、本発明の活性陰極において、特に、逆電流に対する強度が高くなり、活性が低下することがないという現象が知見された。この理由は明らかでないが、運転中の白金またはルテニウムは水素を多量吸蔵しており、逆電流が流れた時は、その吸蔵水素が酸化され、活性の高い表面部分の劣化を抑制することができるものと推定される。また、白金及びルテニウムは化学的安定性に優れ、白金は酸化雰囲気においても容易に酸化されず、また、ルテニウムは、その一部が酸化ルテニウムとなった場合でも再通電することにより容易にルテニウムに還元され再活性化されるため、活性を安定に維持でき低水素過電圧を保持することができるものと推定される。また、第二層の白金及びルテニウムの上記特性は第一層の形態や成分によることがない。これらの現象は、従来、全く知られておらず、発明者らにより初めて知見されたものである。
【００１１】
本発明の活性陰極は、上記したように従来から活性陰極として提案されている金属基体上に形成されるニッケルまたはコバルト主体の被膜を第一層とすることにより、その表面上に白金またはルテニウムの第二層を形成被覆するものである。本発明の第二層は、白金塩またはルテニウム塩の水溶液に上記の従来公知の活性陰極を浸漬し、または浸漬し、更に電解処理することにより形成することができる。
金属基体上に形成された第一層が金属ニッケルを主体とする場合は、その第一層を有する陰極基体を白金またはルテニウム塩水溶液に浸漬することにより、イオン化傾向の差違により白金またはルテニウムイオンが還元され、第一層上に白金またはルテニウムが析出され、第二層を形成することができる。また、ニッケル金属を主体とする第一層上に多量の白金またはルテニウムを析出させる場合、また、第一層が酸化ニッケル、酸化コバルト等の金属ニッケルを主体としない場合は、白金またはルテニウム塩水溶液に浸漬し、その後、第一層を有する陰極基体を陰極として電解処理し、第一層上に微細粒子の白金またはルテニウムの第二層を電気メッキ形成することができる。本発明の方法で形成される第二層は、広大な表面積を有する第一層上に形成されるため、広大な表面積を有することになり好ましい。
【００１２】
本発明で使用する白金塩は、特に制限されるものでなく、三塩化白金、四塩化白金、テトラクロロ白金酸塩、ヘキサクロロ白金酸酸塩、テトラブロモ白金酸塩、ヘキサヨード白金酸塩、ビス（オキサラト）白金酸塩、クロロペンタアンミン白金塩、テトラクロロジアンミン白金等が使用できる。また、ルテニウム塩も特に制限されるものでなく、三塩化ルテニウム３水和物、硫酸ルテニウム、ヘキサクロロルテニウム酸塩、ペンタクロロニトロシルルテニウム酸塩、トリクロロジアクアニトロシルルテニウム３水和物、ルテニウム酸塩、過ルテニウム酸塩等が使用できる。
本発明の溶液は、上記白金またはルテニウム塩を水、酸、アルカリ等の適当な溶媒に溶解して調製する。通常、水溶液が用いられる。この溶液の白金またはルテニウム塩濃度は、第一層の種類、析出させる白金またはルテニウムの量、イオン化傾向差の利用または電解処理等の第二層形成法により変化するため一概には定められないが、通常、１０−６モル／リットル〜１モル／リットル、好ましくは１０−５モル／リットル〜１０−１モル／リットルがよい。白金またはルテニウム塩溶液の濃度が１０−６モル／リットルより薄い場合は、第一層を白金処理するのに時間がかかり過ぎたり、大量の溶液を使用しなくてはならない等の問題があり好ましくなく、一方、白金またはルテニウム塩溶液の濃度が１モル／リットルより濃い場合は、第一層の白金処理速度が速すぎ、所定の厚みの白金層を得るのが困難といった問題があり好ましくない。
【００１３】
本発明の活性陰極に使用される白金またはルテニウムの量は、第一層の種類、水素過電圧の目標値、第二層形成方法等により変化するため一概には定められないが、通常、陰極の投影面積１ｍ２ 当たり１〜５０ｇであり、好ましくは２〜２０ｇである。第二層の白金またはルテニウム量が陰極の投影面積１ｍ２ 当たり１ｇ未満の場合は、水素過電圧の改良効果が十分でない場合があり、また、イオン交換膜のニッケル汚染防止が不十分であることがあり好ましくない。また、５０ｇより多い場合は、使用する白金またはルテニウムに見合うだけの水素過電圧低下の効果を得ることができないためである。
【００１４】
【実施例】
本発明について実施例に基づき、更に詳細に説明する。但し、本発明は、下記の実施例に制限されるものでない。
実施例１〜４及び比較例１
（金属基体上へ第一層の製造：陰極基体の製造）
ニッケル製エキスパンドメタル（２０ｍｍ×２０ｍｍ）を苛性ソーダ溶液で脱脂後、水洗しさらに塩酸（１＋１）でエッチングした。水洗後、表１に示す条件でニッケル基体上にラネーニッケルを主体とする活性陰極を分散メッキ法で形成した。ニッケル基体上に分散メッキしたものを水洗後、２０％苛性ソーダ溶液に７０〜８０℃で２時間浸漬し、アルミニウム分を除去してニッケル基体上にラネーニッケルの第一層を形成した。
上記のような操作を１０バッチ行い合計１０本のラネーニッケル第一層を有する陰極基体サンプルを作製した。陰極基体サンプルの表面粗度を二重層容量法で測定したところ、平均１３３０ｍ２ ／ｍ２ であった。
【００１５】
【表１】

Figure 0003612365
【００１６】
（白金第二層形成）
上記により得られた陰極基体サンプルの８本を２本一組として、それぞれ下記のように電解処理してラネーニッケル第一層上に白金（Ｐｔ）層を電気メッキにより形成した。即ち、各陰極基体サンプルを陰極、ニッケル板を陽極として、２０％苛性ソーダに浸し、温度２０〜２５℃、電流密度３０Ａ／ｄｍ２ 、処理時間２０分の条件下で処理し、各組の陰極基体サンプル上にそれぞれ白金層が２、５、１０及び２０ｇ／ｍ２ で電気メッキ形成された。白金層の析出量は、２０％苛性ソーダ溶液へのヘキサクロロ白金酸添加量を変化させて調節した。
【００１７】
（水素過電圧の測定）
上記のようにして作製されたニッケル金属基体上にラネーニッケル第一層及び白金第二層を有する活性陰極について、水素過電圧をカレントインタラプター法で測定した。測定条件は、温度８０℃、ＮａＯＨ３２％、電流密度３０Ａ／ｄｍ２ 、参照電極Ｈｇ／ＨｇＯ（３２％ＮａＯＨ）であった。また、第１回の測定後、各活性陰極を水洗し、その後大気中室温で一夜（１２時間）放置し、再度同一条件で第２回水素過電圧を測定した。各測定結果を表２に示した。
また、電解処理しなかったニッケル金属基体上にラネーニッケル第一層を有する陰極基体サンプル１本についても同様に水素過電圧を測定し、その結果を表２に示した（比較例１）。
【００１８】
【表２】
Figure 0003612365
【００１９】
実施例４〜７及び比較例２
実施例１と同様にして陰極基体を１０本を製造した。得られた陰極基体サンプルの表面粗度は同様に測定して、平均１３７０ｍ２ ／ｍ２ であった。
また、ヘキサクロロ白金酸の代わりにルテニウム酸ソーダを用いた以外は、実施例１〜４と同様に行い、第二層としてルテニウム層を析出形成した。
上記のようにして作製されたニッケル金属基体上にラネーニッケル第一層及びルテニウム第二層を有する活性陰極について、実施例１と同様に水素過電圧を第１回及び第２回の測定を行った。その測定結果を表３に示した。
また、電解処理しなかったニッケル金属基体上にラネーニッケル第一層を有する陰極基体サンプルについても同様に水素過電圧を測定し、その結果を表３に示した（比較例２）。
【００２０】
【表３】
Figure 0003612365
【００２１】
上記実施例及び比較例から明らかなように、本発明の白金またはルテニウムの第二層を有する活性陰極は、従来のものに比し水素過電圧が低下し、更に、水洗して再使用する場合は、従来のものが水素過電圧が上昇するのに対し、本発明の活性陰極では上昇しないことが分かる。
【００２２】
実施例９〜１２及び比較例３
実施例１〜４で作製した残り４本の各活性陰極サンプルを、実施例１と同様に水素過電圧を測定した。水素過電圧を測定後、活性陰極サンプルを陰極、ニッケル板を陽極として、温度８０℃、電流密度５０Ａ／ｄｍ２ 、苛性ソーダ濃度３２％で、３０分間正規の電解処理を行い、その後、活性陰極を陽分極化して同一条件下で、９分間逆電流試験を実施した。その後、更に再度正規の電解処理を１２０分間行った後、同様に水素過電圧を測定した。逆電流試験前後で測定した各水素過電圧を表４に示した。なお、比較例１のニッケル金属基体上にラネーニッケル第一層を有する残りの従来の活性陰極についても同様に逆電流試験前後の水素過電圧を測定し、表４に併せて示した（比較例３）。
【００２３】
【表４】
Figure 0003612365
【００２４】
実施例１３〜１６及び比較例４
実施例５〜８で作製した残り４本の各活性陰極サンプルを、実施例９と同様に逆電流試験前後で水素過電圧を測定した。逆電流試験前後で測定した各水素過電圧を表５に示した。なお、比較例２のニッケル金属基体上にラネーニッケル第一層を有する残りの従来の活性陰極についても同様に逆電流試験前後の水素過電圧を測定し、表５に併せて示した（比較例４）。
【００２５】
【表５】
Figure 0003612365
【００２６】
実施例１７及び比較例５
ニッケル製エキスパンドメタル（１００ｍｍ×１００ｍｍ）をニッケル製枠に溶接したものを２つ作製し、枠にビニールテープを張り電気的に不導体にした。ニッケル製エキスパンドメタル部を実施例１と同様にして、ラネーニッケル層を形成した。得られたラネーニッケル層形成電解室サンプル２つのうちの一つは、水洗後、乾燥させることなく２０％苛性ソーダとヘキサクロロ白金酸溶液の混合液に、電解室を浸漬し、イオン化傾向差による白金層を析出形成した。白金濃度分析より２．０ｇ／ｍ２ の白金が析出していた。残りの電解室サンプルは比較例として、第一層のみとした。
得られた２つの各電解室サンプルを水洗し乾燥させずに、陰極室として用いて下側にセットし、その上にＥＰＤＭ（エチレンプロピレンゴム）製ガスケット、２％重曹溶液で処理した商品名：ナフィオン９６２の陽イオン交換膜（デュポン社製）、ＰＶＤＦ（ポリフッ化ビニリデン）製ガスケット、商品名ＤＳＡの電極（ペルメレック社製）を溶接したチタン製枠の陽極室を載置して各電解槽を組立て、密封状態にして７日間放置した。
放置後、得られた各電解槽を用いて、温度８０℃、電流密度５０Ａ／ｄｍ２ 、苛性ソーダ濃度３２％、淡塩水濃度２００ｇ／リットルで、３日間電解処理した。その後、各電解槽を解体しイオン交換膜を観察した。その結果、白金層を形成しない陰極室（比較例５）を使用したイオン交換膜は、エキスパンドメタル形の黒い色がついていたが、白金層を形成した陰極室を使用したイオン交換膜は黒色の部分が皆無であった。
【００２７】
実施例１８
ヘキサクロロ白金酸溶液の代わりにルテニウム酸ソーダ溶液を用いて、２０％苛性ソーダとルテニウム酸ソーダ溶液の混合液とした以外は、実施例１７と同様にしてラネーニッケル第一層上にルテニウム第二層を形成した電解室を製造した。この得られたルテニウム第二層を有する電解室を陰極として用いた以外は、実施例１７と全く同様にして電解槽を組立て、同様に電解処理し、その後電解槽を解体して陰極側イオン交換膜を観察した。その結果、同様にイオン交換膜は汚染されていなかった。
【００２８】
実施例１９〜２４及び比較例６
ニッケル製エキスパンドメタル（１００ｍｍ×１００ｍｍ）をトリクレンで脱脂した後、アルミナでブラスト処理し、更に特公平３−４４１５４号公報の実施例１と同様の操作により、酸化ニッケルよりなる活性層を調製した。この酸化ニッケル層の表面粗度を二重層容量法で測定したところ、平均１２１０ｍ２ ／ｍ２ であった。
得られた酸化ニッケル層を有するエキスパンドメタルをニッケル枠内に溶接し陰極室を作製した。このようにして得られた２つの陰極室の酸化ニッケル層上に、実施例１〜３及び実施例５〜７と同様にして、それぞれ白金及びルテニウム層を形成した。得られた各陰極室を使用し、単極式小型電解槽（極間距離２ｍｍ）を組立てた。イオン交換膜としてナフィオン９６２を使用し、温度９０℃、電流密度３０Ａ／ｄｍ２ 、苛性ソーダ濃度３２％、淡塩水濃度２００ｇ／リットルで、３０日間電解処理した。各単極式小型電解槽での電解電圧を測定し、表６に示した。
また、比較例としてニッケル基体上に酸化ニッケル層を有するものを陰極室に用いて電解評価した。その結果を表６に併せて示した（比較例６）。
【００２９】
【表６】
Figure 0003612365
【００３０】
上記実施例及び比較例より、本発明の基板上の酸化ニッケル層上に白金層またはルテニウム層を有する活性陰極の方が、金属基板と酸化ニッケル層の二層からなる活性陰極より幾分ではあるが電解電圧が低下すること、また、白金またはルテニウムの析出量が増加するにつれて、電解電圧が低下することが分かる。
【００３１】
実施例２５〜３０及び比較例７
ニッケル製エキスパンドメタル（１００ｍｍ×１００ｍｍ）をトリクレンで脱脂した後、アルミナでブラスト処理し、更に特公平３−４４１５４号公報の実施例１と同様の操作により、酸化コバルトよりなる活性層を調製した。この酸化コバルト層の表面粗度を二重層容量法で測定したところ、平均１０７０ｍ２ ／ｍ２ であった。
得られた酸化コバルト層を有するエキスパンドメタルをニッケル枠内に溶接し陰極室を作製した。このようにして得られた２つの陰極室の酸化コバルト層上に、実施例１〜３及び実施例５〜７と同様にして、それぞれ白金及びルテニウム層を形成した。得られた各陰極室を使用し、単極式小型電解槽（極間距離２ｍｍ）を組立て、実施例１９〜２４と同様に電解処理した。各単極式小型電解槽での電解電圧を測定し、表７に示した。
また、比較例としてニッケル基体上に酸化コバルト層を有するものを陰極室に用いて電解評価した。その結果を表７に併せて示した（比較例７）。
【００３２】
【表７】
Figure 0003612365
【００３３】
上記実施例及び比較例より、本発明の基板上の酸化コバルト層上に白金層またはルテニウム層を有する活性陰極の方が、酸化コバルト層のみの活性電極より電解電圧が低下すること、また、白金またはルテニウムの析出量が増加するにつれて、電解電圧が低下することが分かる。
【００３４】
比較例８〜９
実施例１で用いたニッケル製エキスパンドメタルを、実施例１と同様に苛性ソーダ溶液で脱脂、水洗、塩酸エッチングした。水洗後、得られた処理エキスパンドメタルの表面粗度を二重層容量法で測定したところ、平均１３ｍ２ ／ｍ２ であった。この処理エキスパンドメタル表面に、実施例３〜４及び実施例７〜８と同様に電解処理して、それぞれ電気メッキの白金析出量が１０、２０ｇ／ｍ２ のもの、ルテニウム析出量が１０、２０ｇ／ｍ２ のものを各１枚ずつ作製した。
得られた各ニッケル基板上に白金層及びルテニウム層を形成したものを陰極として、実施例１９と同様に単極式小型電解槽を組立て、同様に電解処理した。電解処理時の水素過電圧は、それぞれ白金析出量が１０、２０ｇ／ｍ２ のものが１５０ｍＶ、１２０ｍＶであり、ルテニウム析出量が１０、２０ｇ／ｍ２ のものが２５０ｍＶ、２２０ｍＶであった。更に、電解処理後、陰極を観察するといずれも白金及びルテニウムが一部剥離し、ニッケル基体が見える状態であった。
【００３５】
【発明の効果】
本発明の活性陰極は、従来公知の金属基板上にニッケル系またはコバルト系の被膜を形成した活性陰極において、更に、その表面上に化学的安定な白金またはルテニウム層、特に広大な陰極作動表面積を有するように形成するため、水素過電圧が低下し、活性を安定に維持することができる。また、イオン交換膜のニッケル汚染がなくなり、電解処理の停止や電解槽の解体時に、逆電流や空気中での酸化による陰極の劣化もなく極めて有用である。また、溶射法で形成した従来の酸化ニッケルや酸化コバルト被膜を有する活性陰極の水素過電圧を低下させることができ、従来の活性陰極の利用でき簡便に製造することができる。[0001]
[Industrial application fields]
The present invention relates to an active cathode and a method for producing the same, and more particularly to an active cathode capable of electrolyzing an aqueous solution of an alkali metal salt such as an alkali metal halide or an alkali metal hydroxide with a low hydrogen overvoltage for a long time and a method for producing the same.
[0002]
[Prior art]
In the case of electrolyzing an alkali metal halide aqueous solution or an alkali metal hydroxide aqueous solution by a diaphragm method, an ion exchange membrane method or the like, conventionally, a material mainly composed of soft iron is used as a cathode. In these electrolysis, hydrogen is generated at the cathode, and soft iron has a drawback of high hydrogen overvoltage. Therefore, various active cathodes having a hydrogen overvoltage lower than that of a cathode mainly composed of soft iron have been proposed. Conventionally proposed active cathodes use nickel, cobalt, platinum group metal simple substance or a mixture thereof or oxides thereof as a material. Generally, a coating of these materials is formed on a metal substrate such as soft iron. As a method for forming a coating film, an electroplating method, an electroless plating method, a dispersed electroplating method, a thermal spraying method, a dipping method, and the like have been proposed. For example, an active cathode (Japanese Examined Patent Publication No. 61-12032, Japanese Examined Publication No. 61-36590) or a thermal sprayed nickel oxide or cobalt oxide (Japanese Examined Publication No. Sho 63-64518) in which Raney nickel alone or Raney nickel and a hydrogen storage alloy are plated. And Japanese Patent Publication No. 3-35387).
[0003]
[Problems to be solved by the invention]
In the active cathode, the most important point is that the overvoltage can be kept low, and it does not deteriorate when the electrolytic cell is stopped or disassembled. This means that the film is not contaminated by a coating material such as nickel, and the manufacturing cost is low.
However, in the conventionally proposed low hydrogen overvoltage, for example, the Raney nickel alone or an active cathode plated with a composite metal of Raney nickel and a hydrogen storage alloy retains a low hydrogen voltage. There is a drawback that the active cathode is oxidized and ignited or deteriorated by disassembling the cell and contacting the active cathode with air. In addition, when nickel oxide or cobalt oxide is sprayed, the electrolytic cell is disassembled and the active cathode does not deteriorate due to oxidation even if it comes into contact with air. There is a drawback that it rises over time.
[0004]
Conventionally, as one of active cathodes exhibiting a low hydrogen overvoltage, the formation of a coating with a platinum group metal has been proposed, but the surface of a smooth metal base is simply covered with the platinum group. Adhesion with platinum group metals such as platinum and ruthenium is weak, and the platinum group metal coating is easily peeled off from the substrate. In addition, in order to increase the surface activity, a large amount of platinum group metal is required and there is an economic problem. Thus, in the past, active cathodes mainly composed of platinum group metal have not been sufficiently studied. It is.
In view of the current state of the conventional active cathode described above, the present invention provides an active cathode that is free from contamination of the ion exchange membrane, has no risk of deterioration or ignition due to an oxidation reaction, and can maintain a sufficiently low hydrogen overvoltage. The purpose is to provide the law. It is another object of the present invention to provide an active cathode and a method for manufacturing the same, which maintain the advantages of the conventionally proposed active electrode while eliminating the disadvantages. That is, for example, for an active cathode in which Raney nickel alone or Raney nickel and a hydrogen storage alloy is compositely plated, nickel contamination of the ion exchange membrane can be prevented, and oxidation of the active cathode can be suppressed even during disassembly of the electrolytic cell to prevent ignition and deterioration. It is also possible to reduce the hydrogen overvoltage with respect to the active cathode coated with nickel oxide or cobalt oxide.
[0005]
[Means for Solving the Problems]
According to the present invention, an active cathode characterized in that a first layer mainly composed of nickel or cobalt is formed on a metal substrate, and a second layer mainly composed of platinum or ruthenium is formed on the first layer. Is provided.
In the active cathode of the present invention, it is preferable that the first layer is formed with Raney nickel and the second layer has a large cathode working area. Preferably, the first layer is formed of nickel oxide or cobalt oxide, and the second layer is formed of fine platinum particles or ruthenium particles and has a large cathode working area. The ruthenium particles are preferably 0.001 to 0.01 μm. Further, the cathode operating area is 1 m of the projected area of the cathode. 2 It is preferable that it is 30 to 3000 times.
In the present invention, a cathode substrate in which a first layer mainly composed of metallic nickel is formed on a metal substrate is dipped in a solution of platinum salt or ruthenium salt so that platinum or ruthenium is deposited on the first layer. Provided is a method for producing an active cathode, characterized by covering a second layer as a main component.
Further, according to the present invention, a cathode substrate in which a first layer mainly composed of nickel or cobalt is formed on a metal substrate is dipped in a solution of a platinum salt or a ruthenium salt, and further subjected to an electrolytic treatment to perform the first layer There is provided a method for producing an active cathode, characterized in that a second layer mainly composed of platinum or ruthenium is coated thereon.
In the method for producing an active cathode of the present invention, the first layer is preferably formed by an electroplating method, an electroless plating method, a dispersed electroplating method, a thermal spraying method, or an immersion method.
In the present invention, the cathode operating area means the surface area of a portion that can substantially operate as a cathode, unlike the apparent area (projected area) of the cathode.
[0006]
[Action]
The active cathode of the present invention is constituted as described above. In particular, a first layer mainly composed of nickel or cobalt such as Raney nickel or cobalt oxide is formed on a metal substrate, and further, chemically stable platinum or ruthenium. In addition, if necessary, the second layer is formed with fine platinum particles or ruthenium particles to cover the surface of the first layer, so that the cathode operating area is large and a low hydrogen overvoltage can be maintained. In addition, since the cathode surface having a high surface area such as Raney nickel is coated, nickel contamination of the ion exchange membrane can be prevented, and the nickel-based surface having high reaction activity is oxygenated even when the electrolytic cell is stopped or disassembled. Since there is no contact with the cathode, there is no deterioration of the cathode.
In the active cathode of the present invention, the first layer formed of nickel oxide or cobalt oxide in a surface state with poor activity has a relatively high hydrogen overvoltage. Since it is coated with platinum particles or ruthenium particles, the hydrogen overvoltage can be reduced.
In the active cathode of the present invention, platinum is not easily oxidized even when a so-called reverse current flows when the electrolytic cell is stopped and the cathode is positively polarized, and ruthenium is oxidized but is easily reduced by re-energization. Since it is ruthenium, the activity is stable without loss. Since both platinum and ruthenium have better chemical durability than nickel, the ion exchange membrane can be prevented from nickel contamination by covering the nickel-based first layer with platinum or ruthenium. .
Furthermore, the active cathode of the present invention is formed after a first layer is formed on a metal substrate by a conventionally known method such as electroplating or dispersion plating, and further immersed in a solution of platinum or ruthenium salts, or after immersion. By electrolytic treatment, a second layer having a large cathode working area can be formed, and a more stable active cathode with a low hydrogen overvoltage can be obtained using a conventional active cathode.
[0007]
Hereinafter, the present invention will be described in detail.
The material of the metal substrate used in the present invention is not particularly limited, and usually stainless steel, nickel, cobalt, and steel can be used. Further, the structure of the metal substrate may be a flat plate shape, an expanded metal shape, a perforated plate shape, a net shape, a rod shape, or the like, and is not particularly limited.
[0008]
The first layer of the present invention is a layer mainly composed of nickel or cobalt formed on the metal substrate, and a layer formed in the same manner as the conventionally proposed active cathode can be used. The first layer mainly composed of nickel includes Raney nickel, a layer formed of Raney nickel and a hydrogen storage alloy, a nickel alloy layer such as a nickel and tin alloy, a nickel and chromium alloy, sulfur-containing nickel, activated carbon, and sulfur. A surface layer as a conventional nickel-based active cathode such as a layer of nickel containing other components such as nickel or a nickel oxide layer can be used. A surface layer formed of Raney nickel, Raney nickel and a hydrogen storage alloy is preferable because it has a high surface area and high activity. As the first layer mainly composed of cobalt, a surface layer of an active cathode of a conventionally proposed cobalt oxide layer can be used.
The first layer can be formed by a normal electroplating method, electroless plating method, dispersion electroplating method, thermal spraying method or immersion method, and may be appropriately selected according to the constituent components of nickel or cobalt. The thickness of the first layer may be 10 to 500 μm and can be appropriately selected. Usually, it is 50-300 micrometers.
[0009]
The second layer of the active cathode of the present invention is a layer formed by coating the surface of the first layer with platinum group metal platinum or ruthenium. The second layer is obtained by immersing or soaking the so-called conventional active cathode in which the first layer is formed on a metal substrate in an aqueous solution in which platinum or ruthenium salts are dissolved as described below. Can be formed. In the present invention, the surface of the first layer mainly composed of nickel is coated with a second layer composed of platinum and ruthenium, so that platinum and ruthenium have better chemical durability than nickel, and the ion exchange membrane is protected from nickel contamination. Can be avoided.
The second layer of the active cathode of the present invention preferably has a large cathode working area, and for this purpose, it is formed to have a high surface area. A vast cathode working area means a surface area that operates substantially as a cathode, per unit area in appearance of the active cathode, that is, a projected area of 1 m of the cathode. 2 The surface area is preferably about 30 to 3000 times as large as that of the surface area. Since the active cathode of the present invention has a large surface area as described above, the cathode working area is increased, so that the cathode current density is substantially reduced, and as a result, the hydrogen overvoltage can be reduced.
The vast surface area of the second layer of the present invention is appropriately selected depending on the form of the lower first layer. For example, when the first layer is an oxide system of nickel oxide or cobalt oxide, it is generally 0.001. The fine platinum particles or ruthenium particles of ˜0.01 μm can be formed by coating using a method such as electrolysis in an aqueous solution in which platinum or ruthenium salts are dissolved. In addition, when the first layer is a layer containing Raney nickel or Raney nickel and Raney nickel such as a hydrogen storage alloy, the first layer itself has a high surface area, and a platinum or ruthenium coating of the second layer is formed on the surface of platinum or ruthenium. A second layer having a vast surface area can be formed by immersing in an aqueous solution in which salts are dissolved or by performing an electrolytic treatment by immersing the salt.
[0010]
The active cathode of the present invention is such that a first layer mainly composed of nickel or cobalt and a second layer of platinum or ruthenium are sequentially formed on a metal substrate as described above. That is, the first layer is covered with platinum group metal platinum or ruthenium, and the cathode surface is replaced with highly active and stable platinum or ruthenium, so that the hydrogen overvoltage is significantly reduced.
In addition, in the active cathode of the present invention, it has been found that the strength against reverse current is particularly high and the activity does not decrease. The reason for this is not clear, but platinum or ruthenium in operation stores a large amount of hydrogen, and when a reverse current flows, the stored hydrogen is oxidized, and deterioration of the surface portion with high activity can be suppressed. Estimated. In addition, platinum and ruthenium are excellent in chemical stability, and platinum is not easily oxidized even in an oxidizing atmosphere, and ruthenium is easily converted into ruthenium by re-energizing even when part of it becomes ruthenium oxide. Since it is reduced and reactivated, it is presumed that the activity can be stably maintained and a low hydrogen overvoltage can be maintained. Further, the above characteristics of platinum and ruthenium in the second layer do not depend on the form or components of the first layer. These phenomena have not been known at all in the past, and were first discovered by the inventors.
[0011]
As described above, the active cathode of the present invention has a nickel or cobalt-based coating formed on a metal substrate, which has been conventionally proposed as an active cathode, as a first layer so that platinum or ruthenium is formed on the surface thereof. The second layer is formed and coated. The second layer of the present invention can be formed by immersing or immersing the above-mentioned conventionally known active cathode in an aqueous solution of platinum salt or ruthenium salt, and further electrolytically treating it.
When the first layer formed on the metal substrate is mainly composed of metallic nickel, the cathode substrate having the first layer is immersed in an aqueous solution of platinum or ruthenium salt, so that platinum or ruthenium ions are caused by the difference in ionization tendency. Reduction and platinum or ruthenium are deposited on the first layer to form a second layer. When a large amount of platinum or ruthenium is deposited on the first layer mainly composed of nickel metal, or when the first layer is not mainly composed of nickel metal such as nickel oxide or cobalt oxide, an aqueous solution of platinum or ruthenium salt is used. Then, the cathode substrate having the first layer is electrolyzed as a cathode, and a second layer of fine particles of platinum or ruthenium can be electroplated on the first layer. Since the second layer formed by the method of the present invention is formed on the first layer having a large surface area, it preferably has a large surface area.
[0012]
The platinum salt used in the present invention is not particularly limited, and platinum trichloride, platinum tetrachloride, tetrachloroplatinate, hexachloroplatinate, tetrabromoplatinate, hexaiodoplatinate, bis (oxalato) ) Platinum salts, chloropentammine platinum salts, tetrachlorodiammine platinum and the like can be used. Also, the ruthenium salt is not particularly limited, and ruthenium trichloride trihydrate, ruthenium sulfate, hexachlororuthenate, pentachloronitrosylruthenate, trichlorodiaquanitrosylruthenium trihydrate, ruthenate, Perruthenate can be used.
The solution of the present invention is prepared by dissolving the platinum or ruthenium salt in a suitable solvent such as water, acid, alkali or the like. Usually, an aqueous solution is used. The platinum or ruthenium salt concentration of this solution is not generally determined because it varies depending on the type of the first layer, the amount of platinum or ruthenium to be deposited, the use of ionization tendency differences, or the second layer formation method such as electrolytic treatment. Usually 10 -6 Mol / liter to 1 mol / liter, preferably 10 -5 Mol / liter to 10 -1 Mole / liter is preferred. The concentration of platinum or ruthenium salt solution is 10 -6 If it is thinner than mol / liter, it is not preferable because it takes too much time to treat the first layer with platinum or a large amount of solution must be used. On the other hand, the concentration of the platinum or ruthenium salt solution is undesirable. Is higher than 1 mol / liter, it is not preferable because the platinum treatment speed of the first layer is too high and it is difficult to obtain a platinum layer having a predetermined thickness.
[0013]
The amount of platinum or ruthenium used in the active cathode of the present invention varies depending on the type of the first layer, the target value of the hydrogen overvoltage, the method of forming the second layer, etc. Projection area 1m 2 1 to 50 g per unit, preferably 2 to 20 g. The amount of platinum or ruthenium in the second layer is 1 m in projected area of the cathode. 2 If it is less than 1 g per unit, the effect of improving the hydrogen overvoltage may not be sufficient, and the nickel contamination of the ion exchange membrane may be insufficiently prevented, which is not preferable. On the other hand, when the amount is more than 50 g, the effect of lowering the hydrogen overvoltage sufficient for the platinum or ruthenium used cannot be obtained.
[0014]
【Example】
The present invention will be described in more detail based on examples. However, the present invention is not limited to the following examples.
Examples 1 to 4 and Comparative Example 1
(Manufacture of first layer on metal substrate: manufacture of cathode substrate)
Nickel expanded metal (20 mm × 20 mm) was degreased with a caustic soda solution, washed with water, and further etched with hydrochloric acid (1 + 1). After washing with water, an active cathode mainly composed of Raney nickel was formed on the nickel substrate by the dispersion plating method under the conditions shown in Table 1. What was dispersedly plated on the nickel substrate was washed with water and then immersed in a 20% caustic soda solution at 70 to 80 ° C. for 2 hours to remove aluminum and form a first layer of Raney nickel on the nickel substrate.
The cathode base sample having a total of 10 Raney nickel first layers was prepared by carrying out 10 batches as described above. When the surface roughness of the cathode substrate sample was measured by the double layer capacitance method, the average was 1330 m. 2 / M 2 Met.
[0015]
[Table 1]
Figure 0003612365
[0016]
(Platinum second layer formation)
A set of two cathode substrate samples obtained as described above was subjected to electrolytic treatment as follows, and a platinum (Pt) layer was formed on the first Raney nickel layer by electroplating. That is, each cathode substrate sample was immersed in 20% caustic soda using a nickel plate as an anode, a temperature of 20 to 25 ° C., and a current density of 30 A / dm. 2 The platinum layer is 2, 5, 10 and 20 g / m on each set of cathode substrate samples. 2 With electroplating formed. The amount of platinum layer deposited was adjusted by changing the amount of hexachloroplatinic acid added to the 20% sodium hydroxide solution.
[0017]
(Measurement of hydrogen overvoltage)
The hydrogen overvoltage was measured by the current interrupter method for the active cathode having the Raney nickel first layer and the platinum second layer on the nickel metal substrate produced as described above. Measurement conditions are temperature 80 ° C., NaOH 32%, current density 30 A / dm. 2 The reference electrode was Hg / HgO (32% NaOH). In addition, after the first measurement, each active cathode was washed with water and then left overnight in the atmosphere at room temperature (12 hours), and the second hydrogen overvoltage was measured again under the same conditions. The measurement results are shown in Table 2.
Further, hydrogen overvoltage was measured in the same manner for one cathode substrate sample having a Raney nickel first layer on a nickel metal substrate that was not subjected to electrolytic treatment, and the results are shown in Table 2 (Comparative Example 1).
[0018]
[Table 2]
Figure 0003612365
[0019]
Examples 4 to 7 and Comparative Example 2
Ten cathode substrates were produced in the same manner as in Example 1. The surface roughness of the obtained cathode substrate sample was measured in the same manner, and averaged 1370 m. 2 / M 2 Met.
Moreover, it carried out similarly to Examples 1-4 except having used sodium ruthenate instead of hexachloroplatinic acid, and deposited and formed the ruthenium layer as a 2nd layer.
For the active cathode having the Raney nickel first layer and the ruthenium second layer on the nickel metal substrate produced as described above, the hydrogen overvoltage was measured first and second times in the same manner as in Example 1. The measurement results are shown in Table 3.
Further, a hydrogen overvoltage was measured in the same manner for a cathode substrate sample having a Raney nickel first layer on a nickel metal substrate not subjected to electrolytic treatment, and the results are shown in Table 3 (Comparative Example 2).
[0020]
[Table 3]
Figure 0003612365
[0021]
As is clear from the above Examples and Comparative Examples, the active cathode having the second layer of platinum or ruthenium according to the present invention has a reduced hydrogen overvoltage compared to the conventional one, and further, when it is reused after washing with water. It can be seen that the hydrogen overvoltage increases in the conventional device, but does not increase in the active cathode of the present invention.
[0022]
Examples 9-12 and Comparative Example 3
The hydrogen overvoltage was measured for the remaining four active cathode samples prepared in Examples 1 to 4 in the same manner as in Example 1. After measuring the hydrogen overvoltage, the active cathode sample was the cathode, the nickel plate was the anode, the temperature was 80 ° C., and the current density was 50 A / dm. 2 Then, a normal electrolytic treatment was performed for 30 minutes at a caustic soda concentration of 32%, and then a reverse current test was performed for 9 minutes under the same conditions with the active cathode being positively polarized. Thereafter, regular electrolytic treatment was performed again for 120 minutes, and the hydrogen overvoltage was measured in the same manner. Table 4 shows the hydrogen overvoltages measured before and after the reverse current test. The hydrogen overvoltage before and after the reverse current test was measured in the same manner for the remaining conventional active cathode having the Raney nickel first layer on the nickel metal substrate of Comparative Example 1 and is shown in Table 4 (Comparative Example 3). .
[0023]
[Table 4]
Figure 0003612365
[0024]
Examples 13 to 16 and Comparative Example 4
The remaining four active cathode samples prepared in Examples 5 to 8 were measured for hydrogen overvoltage before and after the reverse current test in the same manner as in Example 9. Table 5 shows the hydrogen overvoltages measured before and after the reverse current test. The hydrogen overvoltage before and after the reverse current test was measured in the same manner for the remaining conventional active cathode having the Raney nickel first layer on the nickel metal substrate of Comparative Example 2 and is also shown in Table 5 (Comparative Example 4). .
[0025]
[Table 5]
Figure 0003612365
[0026]
Example 17 and Comparative Example 5
Two pieces of nickel expanded metal (100 mm × 100 mm) welded to a nickel frame were prepared, and vinyl tape was applied to the frame to make it electrically non-conductive. A Raney nickel layer was formed in the same manner as in Example 1 for the nickel expanded metal part. One of the two Raney nickel layer-forming electrolytic chamber samples obtained was immersed in a 20% caustic soda and hexachloroplatinic acid solution without drying after washing with water, and the platinum layer due to the difference in ionization tendency was removed. Precipitation was formed. 2.0g / m from platinum concentration analysis 2 Of platinum was deposited. The remaining electrolytic chamber sample was only the first layer as a comparative example.
The obtained two electrolytic chamber samples were washed with water and not dried, but used as a cathode chamber, set on the lower side, and treated thereon with an EPDM (ethylene propylene rubber) gasket and a 2% sodium bicarbonate solution. Each electrolytic cell was placed by placing a cation exchange membrane of Nafion 962 (manufactured by DuPont), a gasket made of PVDF (polyvinylidene fluoride), and an anode chamber of a titanium frame welded with a DSA electrode (manufactured by Permerek). Assembled and sealed for 7 days.
After standing, using each of the obtained electrolytic cells, temperature 80 ° C., current density 50 A / dm 2 Electrolytic treatment was performed for 3 days at a caustic soda concentration of 32% and a fresh salt water concentration of 200 g / liter. Thereafter, each electrolytic cell was disassembled and the ion exchange membrane was observed. As a result, the ion exchange membrane using the cathode chamber in which the platinum layer was not formed (Comparative Example 5) had an expanded metal type black color, but the ion exchange membrane using the cathode chamber in which the platinum layer was formed was black. There was no part.
[0027]
Example 18
A ruthenium second layer is formed on the Raney nickel first layer in the same manner as in Example 17 except that a sodium ruthenate solution is used instead of the hexachloroplatinic acid solution to obtain a mixed solution of 20% sodium hydroxide and sodium ruthenate solution. An electrolytic chamber was manufactured. Except for using the obtained electrolysis chamber having the ruthenium second layer as the cathode, an electrolytic cell was assembled and electrolyzed in the same manner as in Example 17, and then the electrolytic cell was disassembled and the cathode side ion exchange was performed. The membrane was observed. As a result, the ion exchange membrane was not contaminated as well.
[0028]
Examples 19 to 24 and Comparative Example 6
Nickel expanded metal (100 mm × 100 mm) was degreased with trichrene, then blasted with alumina, and an active layer made of nickel oxide was prepared in the same manner as in Example 1 of JP-B-3-44154. When the surface roughness of the nickel oxide layer was measured by the double layer capacitance method, the average was 1210 m. 2 / M 2 Met.
The obtained expanded metal having a nickel oxide layer was welded into a nickel frame to produce a cathode chamber. Platinum and ruthenium layers were formed on the nickel oxide layers in the two cathode chambers thus obtained in the same manner as in Examples 1 to 3 and Examples 5 to 7, respectively. Using each of the obtained cathode chambers, a single electrode type small electrolytic cell (distance between electrodes: 2 mm) was assembled. Nafion 962 is used as an ion exchange membrane, temperature is 90 ° C., and current density is 30 A / dm. 2 Electrolytic treatment was performed for 30 days at a caustic soda concentration of 32% and a fresh salt water concentration of 200 g / liter. The electrolytic voltage in each single-electrode small electrolytic cell was measured and shown in Table 6.
Further, as a comparative example, electrolytic evaluation was performed using a nickel base layer having a nickel oxide layer as a cathode chamber. The results are also shown in Table 6 (Comparative Example 6).
[0029]
[Table 6]
Figure 0003612365
[0030]
From the above examples and comparative examples, the active cathode having a platinum layer or a ruthenium layer on the nickel oxide layer on the substrate of the present invention is somewhat more active than the active cathode consisting of a metal substrate and a nickel oxide layer. It can be seen that the electrolysis voltage decreases, and that the electrolysis voltage decreases as the amount of platinum or ruthenium deposited increases.
[0031]
Examples 25-30 and Comparative Example 7
Nickel expanded metal (100 mm × 100 mm) was degreased with trichrene, then blasted with alumina, and an active layer made of cobalt oxide was prepared in the same manner as in Example 1 of JP-B-3-44154. When the surface roughness of the cobalt oxide layer was measured by the double layer capacitance method, the average was 1070 m. 2 / M 2 Met.
The obtained expanded metal having a cobalt oxide layer was welded into a nickel frame to produce a cathode chamber. Platinum and ruthenium layers were formed on the cobalt oxide layers in the two cathode chambers thus obtained in the same manner as in Examples 1 to 3 and Examples 5 to 7, respectively. Using each of the obtained cathode chambers, a single electrode type small electrolytic cell (distance between electrodes: 2 mm) was assembled and subjected to electrolytic treatment in the same manner as in Examples 19-24. The electrolytic voltage in each single-electrode small electrolytic cell was measured and shown in Table 7.
Further, as a comparative example, electrolytic evaluation was carried out using a cathode substrate having a cobalt oxide layer on a nickel substrate. The results are also shown in Table 7 (Comparative Example 7).
[0032]
[Table 7]
Figure 0003612365
[0033]
From the above Examples and Comparative Examples, the active cathode having a platinum layer or a ruthenium layer on the cobalt oxide layer on the substrate of the present invention has a lower electrolysis voltage than the active electrode having only the cobalt oxide layer, and platinum. Or it turns out that an electrolysis voltage falls as the precipitation amount of ruthenium increases.
[0034]
Comparative Examples 8-9
The nickel expanded metal used in Example 1 was degreased with a caustic soda solution, washed with water, and etched with hydrochloric acid in the same manner as in Example 1. After washing with water, the surface roughness of the obtained treated expanded metal was measured by the double layer capacity method, and the average was 13 m. 2 / M 2 Met. This treated expanded metal surface was subjected to electrolytic treatment in the same manner as in Examples 3 to 4 and Examples 7 to 8, and the platinum deposition amount of electroplating was 10, 20 g / m, respectively. 2 The ruthenium deposition amount is 10, 20 g / m 2 Each one was prepared.
Using the obtained nickel substrate formed with a platinum layer and a ruthenium layer as a cathode, a monopolar small electrolytic cell was assembled in the same manner as in Example 19 and subjected to electrolytic treatment in the same manner. The hydrogen overvoltage during the electrolytic treatment is such that the amount of deposited platinum is 10 and 20 g / m, respectively. 2 Are 150 mV and 120 mV, and the ruthenium deposition amount is 10, 20 g / m. 2 Were 250 mV and 220 mV. Further, after the electrolytic treatment, when the cathode was observed, platinum and ruthenium were both partially peeled off and the nickel substrate was visible.
[0035]
【The invention's effect】
The active cathode of the present invention is an active cathode in which a nickel-based or cobalt-based film is formed on a conventionally known metal substrate, and further has a chemically stable platinum or ruthenium layer on its surface, in particular a vast cathode working surface area. Since it forms so that it may have, hydrogen overvoltage falls and activity can be maintained stably. Further, nickel contamination of the ion exchange membrane is eliminated, and the cathode is extremely useful when the electrolytic treatment is stopped or the electrolytic cell is dismantled without reverse current or deterioration of the cathode due to oxidation in the air. Further, the hydrogen overvoltage of an active cathode having a conventional nickel oxide or cobalt oxide film formed by thermal spraying can be reduced, and the conventional active cathode can be used and can be easily manufactured.

Claims (7)

金属基体上に、ニッケル系活性陰極又は酸化コバルト層活性陰極の第一層及び該第一層上に白金またはルテニウムの第二層が形成されてなり、該第二層が、陰極の投影面積１ｍ 2 に対し３０〜３０００倍である陰極作動面積を有することを特徴とする活性陰極。On a metal substrate, nickel-based active cathode or second layer of platinum or ruthenium is formed on the first layer and the first layer on the layer of cobalt oxide active cathode Ri name is the second layer, the projected area of the cathode active cathode 1 m 2 to characterized Rukoto that having a cathode working area is 30-3000 times. 前記第一層が、ラネーニッケルを有して形成されてなる陰極作動面積を有する請求項１記載の活性陰極。It said first layer, active cathode according to claim 1, further comprising a cathode working area ing formed with a Raney nickel. 前記第一層が酸化ニッケル又は酸化コバルトを有して形成され、前記第二層が微細な白金粒子又はルテニウム粒子により形成されてなる請求項１記載の活性陰極。Said first layer is formed with a nickel oxide or cobalt oxide, the second layer is the active cathode according to claim 1, wherein ing is formed by fine platinum particles or ruthenium particles. 前記白金粒子又はルテニウム粒子が、０．００１〜０．０１μｍである請求項３記載の活性陰極。The active cathode according to claim 3, wherein the platinum particles or ruthenium particles are 0.001 to 0.01 μm. 金属基体上に金属ニッケル系活性陰極の第一層が形成されてなる陰極基体を、白金塩またはルテニウム塩の溶液に浸漬処理して該第一層上に白金またはルテニウムの第二層を被覆し、該第二層が、陰極の投影面積１ｍ 2 に対し３０〜３０００倍である陰極作動面積を有することを特徴とする活性陰極の製造法。The cathode substrate for the first layer is formed of a metallic nickel-based active cathode on the metal substrate, and immersed in a solution of a platinum salt or ruthenium salt to coat the second layer of platinum or ruthenium to said first layer on the , the second layer, the preparation of active cathode, characterized in that have a cathode working area is 30-3000 times the projected area 1 m 2 of the cathode. 金属基体上にニッケル系活性陰極又はコバルト層活性陰極の第一層が形成されてなる陰極基体を、白金塩またはルテニウム塩の溶液に浸漬し、更に、電解処理して該第一層上に白金またはルテニウムの第二層を被覆し、該第二層が、陰極の投影面積１ｍ 2 に対し３０〜３０００倍である陰極作動面積を有することを特徴とする活性陰極の製造法。A cathode substrate in which a nickel- based active cathode or a cobalt layer active cathode first layer is formed on a metal substrate is immersed in a platinum salt or ruthenium salt solution, and further subjected to electrolytic treatment to form platinum on the first layer. or coated with a second layer of ruthenium, the second layer, the preparation of active cathode, characterized in that have a cathode working area is 30-3000 times the projected area 1 m 2 of the cathode. 前記第一層が、電気メッキ法、無電解メッキ法、分散電気メッキ法、溶射法又は浸漬法により形成される請求項５または６記載の活性陰極の製造法。The method for producing an active cathode according to claim 5 or 6 , wherein the first layer is formed by electroplating, electroless plating, dispersion electroplating, thermal spraying or dipping.
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